This invention relates to an automatic weighing system for delivering quantities of product measured by weight so as to keep both the weight and volume of each delivery within respective allowable ranges.
An example of this type of weighing system is disclosed in U.S. Pat. No. 4,548,286. The patented system was proposed for packing product as cornflakes or potato chips which vary considerably in size and shape and, consequently, in their apparent density or specific gravity, so that both the weight and volume of each pack falls within respective predetermined allowable ranges. To this end, the system uses a combination weighing device including a plurality of weighers for weighing quantities of product representing fractions of the final package amount, for generating combinations of the fractional weights and comparing the combined weights with a predetermined target weight to select a combination satisfying a predetermined weight condition. The system controls the target weight in accordance with an average density of the product measured by an associated apparent density detector.
In this system, the measured average density is compared with a predetermined upper threshold density. The target weight is maintained when the measured density is lower than the upper threshold density. When the former exceeds the latter, however, the target weight is corrected by calculating a difference between the average and threshold densities and adding a product of the difference and a predetermined value to the target weight.
In the above-cited system, the target weight is maintained when the average density is lower than the upper threshold density. Therefore, if the average apparent density should become very low, that is, if the product piece size should become very large, there would be a risk of overflow of product from the package. Although the cited patent also discloses a conditioner for regulating the volume of each delivery, such overflow cannot be avoided since system does not respond to the average apparent density.